A2 Organic Flashcards
what does NMR stand for?
nuclear magnetic resonance
13C NMR gives simpler spectra than 1H NMR
.
what mass number is needed for NMR
odd mass number
what solvents can the sample be dissolved in in 13C NMR & why?
polar solvents dissolve polar molecules & non-polar solvents dissolve non-polar molecules
CCl4 - non-polar molecule
D = 2H = even mass # so will not give signal
CDCl3 - polar molecule
C6D6
these C will give a signal but the value is known so is removed from the spectrum
what substance is used to calibrate the spectrum, what is its structure?
tetramethylsilane
Si(CH3)4 - see booklet
why is TMS used for calibration of spectrum?
it only gives one signal
it is non-toxic
it is inert
it has a low bp so can be easily removed from sample afterwards
it gives a signal that is far right than most signals from organic compounds - this is given the value of 0ppm
in 13C NMR, what is the # of signals based on?
the number of C atoms in different chemical environments
in 13C NMR, what does chemical shift depend on?
what other atoms/groups are near the C
the closer the C is to electronegative atoms (e.g. O, Cl), the greater the chemical shift
the more electronegative atoms near to the C, the greater the chemical shift
what is the relevance of the vertical axis in 13C NMR
it has no relevance
when looking at the table of 13C NMR values,
start at the bottom & work your way up
what is the relevance of the vertical axis in 1H NMR
it shows the intensity of the absorption
in 1H NMR, what is the number of signals based on?
there is one signal for each set of equivalent H atoms (H atoms in equivalent chemical environment)
in 1H NMR, what is the area of each signal based on?
the area of each signal is proportional to the # of equivalent H atoms (H atoms in equivalent chemical environment)
in 1H NMR, what is the integration ratio?
it indicates the relative numbers of H atoms in different environments/equivalent H atoms
for splitting patterns, the number of lines =
1 + the number of inequivalent H atoms on adjacent C atoms
across which atoms is there no splitting?
O
-OH group in alcohols rarely causes splitting or is split itself
sometimes the H of the OH appears as a broad bump
what are the relative heights of peaks in splitting?
singlet
doublet 1:1
triplet 1:2:1
quartet 1:3:3:1
multiplet
what is the number of neighbouring inequivalent H atoms for each splitting signal?
singlet: 0
doublet: 1
triplet: 2
quartet: 3
name the 3 types of chromatography
- thin-layer chromatography
- column chromatography
- gas chromatography
describe thin-layer chromatography
a plate is coated with a solid & a solvent moves up the plate
describe column chromatography
a column is packed with a solid and a solvent moves down the column
describe gas chromatography
a column is packed with a solid or a solid coated by a liquid
a gas is passed through the column under pressure at high temp.
in chromatography, what does separation depend on
the balance b/w solubility in/affinity for the moving phase & retention by the stationary phase
how to calculate Rf value
distance travelled by component / distance travelled by solvent
what is retention time?
time taken for each substance to drain out of the column in column chromatography
the greater the affinity of a molecule to the mobile phase,
the shorter the distance it moves with the mobile phase
describe the method for thin-layer chromatography
metal plate coated with thin layer of powdered silica
components put on plate
pencil start line is drawn
solvent moves up the plate
sealed system to reduce loss of solvent & increase speed
can calculate Rf value
insoluble components stay on pencil line
describe the method for 2d TLC
after the first attempt, rotate the plate 90degrees & use a different solvent
this works well for substances that are insoluble in the first solvent
describe the method for column chromatography
vertical column is filled with a solid, powdered substance usually silica (to increase sa) = stationary phase
solvent that contains the mixture being analysed is added & moves down the column as the mobile phase
the different affinities of molecules in the mixture = they drain out of the column at different times & are collected as separate samples
silica is polar
describe the method for gas chromatography
thin tube is filled with a solid, powdered substance = stationary phase e.g. silica
inert gas carrier = mobile phase @ high pressure & high temp.
separate mixtures of volatile liquids
@ end of column, detectors identify each component & retention time for each compound can be recorded
describe gas chromatography mass spectrometry (GCMS)
type of GC
separated components are ionised as they emerge from column
identity & abundance of each component are measured by MS
GCMS is much faster & more accurate
what is the order of priority of functional groups?
alkenes
haloalkanes
amines
alcohols
ketones
aldehydes
nitriles
amides
acyl chloride
acid anhydride
esters
carboxylic acids
define optical isomerism
a form of stereoisomerism that occurs in molecules with a single chiral carbon centre
what is a chiral carbon atom?
C with 4 different groups attached
asymmetric
what are enantiomers?
2 compounds that are optical isomers
what are optical isomers?
molecules that are non-super imposable mirror images, and have different effects on the plane of polarised light
they have the same chemical & physical properties
what is a racemate/racemic mixture?
a 50/50 mixture of the enantiomers
what effect do optical isomers have on the plane of polarised light?
optical isomers can rotate the plane of polarised light
one enantiomer rotates the plane of polarised light in one direction & the other enantiomer rotates the plane of polarised light by the same amount in the opposite direction
what effect does a racemic mixture have on the plane of polarised light & why?
no effect - they are optically inactive
each enantiomer rotates the plane of polarised light by the same amount in opposite directions, so their effects cancel out
can ketones be oxidised?
no
what are the oxidation equations for:
primary alcohols
aldehydes
secondary alcohols?
see booklet
what are the reduction equations for aldehydes & ketones & what is the reducing agent?
see booklet
NaBH4 provides H- ions
what ion does reduction of aldehydes & ketones produce?
H-
describe the importance of acidified potassium dichromate (K2Cr2O7 & H2SO4)
orange Cr2O7 2- ion are reduced to green Cr3+ ions as they oxidise alcohol/aldehyde
under what conditions is a primary alcohol oxidised to an aldehyde & carboxylic acid?
aldehyde: distillation
carboxylic acid: reflux
what are the tests for an aldehyde & explain red./ox. that happens?
Tollen’s reagent
Ag(NH3)2 + ions reduced to silver mirror
aldehyde is oxidised to carboxylic acid
Fehling’s solution
blue solution forms red precipitate
Cu2+ ions reduced to Cu2O
aldehyde is oxidised to carboxylic acid
what mechanism is involved in reduction?
nucleophilic addition
what are the reagent, conditions, products & overall equation of nucleophilic addition for reduction?
reagent: NaBH4 or LiAlH4
conditions: aqueous or LiAlH4 in ether (any H2O will explode)
products: from aldehydes, 1 alcohols & from ketones, 2 alcohols
overall equation: + 2[H] - see booklet
what is the mechanism for nucleophilic addition for reduction?
see booklet
what are the sources of H- & H+ ions in nuc. add. for reduction?
H- ions: NaBH4
H+ ions: water
what are the reagents, conditions, products & overall equation of nucleophilic addition for addition of HCN?
reagents: KCN followed by dilute strong acid
KCN is ionic & soluble so strong acid provides H+
conditions: aqueous
products: 2-hydroxynitriles
overall equation: + HCN - see booklet
what are the hazards of using KCN?
it is very toxic
why is HCN not the reagent for nuc. add.?
HCN is weak acid so v. low conc. so slow rate
HCN <–> H+ + CN-
what is the mechanism for nucleophilic addition for addition of HCN?
see booklet
what type of mixture is generally formed from nucleophilic addition for addition of HCN & why?
a racemic mixture
the CN- attacks (attaches to) the planar >C=O from above & below with equal probability so forms a 50/50 mixture of enantiomers (optical isomers)
so the product has no effect on the plane of polarised light
what is the effect of 2-hydroxymethylpropanenitrile on the plane of polarised light?
no effect on the plane of polarised light because there is no chiral carbon so not optically active
what type of acids are carboxylic acids?
weak acids - only a small fraction of the molecules dissociate to release H+ ions in water
what do carboxylic acids react with & what is the rate of reaction compared to strong acids?
what stays the same?
alkalis, metals, carbonates, ammonia
slower rate
moles that react are the same
how do you name & draw the salts of carboxylic acids?
e.g. sodium methanoate
take off the H, leaving O-
& put +ve ion next to it with a + sign
what is esterification?
making esters from carboxylic acids reacting with alcohols
describe the reaction for esterification
slow & reversible
conc. acid catalyst
what 3 things are needed for esterification?
alcohol
carboxylic acid
conc. acid
what is the better method of esterification & what are the benefits?
reacting an alcohol & an acid anhydride
reaction is faster & give higher yield
how are acid anhydrides formed?
from 2 carboxylic acids
-H on one & -OH on other are removed & form water
functional group for acid anhydrides: -C=O - O - C=O -
describe ester hydrolysis in acidic conditions
esters can be broken down into carboxylic acid & alcohol
slow & reversible reaction
describe ester hydrolysis in alkali conditions
= saponification
reaction goes to completion
forms salt of carboxylic acid & alcohol
what are the uses of esters?
- food flavouring
- perfumes (contain mixtures of esters in solvents that quickly evaporate)
- used as solvents
- used as plasticisers, which are added to polymers to make them more flexible
what are lipids?
esters
3 long carboxylic acids (fatty acids)
joined through propane-1,2,3-triol (glycerol), which has 3 alcohol groups
what are oils & what do they contain?
lipids that are liquid at room temp.
tend to contain unsaturated fatty acids
what are fats & what do they contain?
lipids that are solid at room temp.
tend to contain saturated fatty acids
define saturated fatty acid
fatty acid with no C=C
monounsaturated vs polyunsaturated fatty acids
mono: contain one C=C
poly: contain more than one C=C
what is saponification?
lipids break down in alkali conditions (in KOH) to form the salts of fatty acids (anionic surfactants = soaps) + glycerol
what is the reagent for the breakdown of lipids into fatty acids + glycerol?
HCl
describe biodiesel production
lipid breaks down into 3 fatty acids & glycerol by reaction with KOH
fatty acids converted into methyl esters using methanol
KOH is a catalyst
what type of fuel can biodiesel be?
carbon neutral
renewable
define carbon neutral
no net annual release of CO2 into the atmosphere
bc same amount CO2 released when fuel is burned as the crops it was made from absorbed for PS
define biofuel
fuel that gives out heat energy made from plants/organic matter
how do soaps work?
fatty acid - hydrophobic
forms VDW forces b/w other long chain alkyl groups
C=O - O-
hydrophilic
O- surrounded by delta + H of water = ionic interaction
compare acylation using carboxylic acids, acid anhydrides & acyl chlorides
carboxylic acids: slow, low yield
acid anhydride: acceptable rate & yield
cheaper
produce a carboxylic acid as a product
acyl chloride: high yield but too vigorous so cannot control reaction
much more expensive
produce corrosive HCl product
what is acylation?
the insertion of an acyl group
what is an acyl group?
r-c=o
what are the reagents, conditions & products of nucleophilic addition-elimination for acylation?
acid anhydride or acyl chloride
from water - carboxylic acid
from alcohols - ester
from ammonia - amide
from amines - n-substituted amide
other product is an acid
what atoms do the acyl group replace on alcohols & water?
H on the O of alcohols/water is replaced by an acyl group
what atoms do acyl groups replace for amine/ammonia?
H on the N of an amine/ammonia is replaced by an acyl group
acylation: with amines/ammonia, what does the acid by-product react with & form?
acid reacts with second molecule of amine/ammonia to form ammonium salt
the acid by-product donates H+ to another molecule of ammonia/amine
what is the mechanism for acylation of ammines/ammonia & alcohols/water with acyl chlorides?
see booklet
what is the structure of benzene?
C6H6
hexagonal ring with 1 H bonded to each C
planar
each C forms 3 covalent bonds
all C-C same length - intermediate b/w single & double bond
how are the e-s arranged in benzene molecule?
one e- on each C atom in p orbital that is perpendicular to plane of the benzene ring
cloud of -ve charge above & below the plane of the ring = spare e-s overlap in pi cloud
ring of delocalised p e-s
what are the 3 pieces of evidence for the delocalised structure of benzene compared with 1,3,5-cyclohexatriene?
- C-C bond length
- addition reactions
- enthalpy of hydrogenation
how does C-C bond length give evidence for the delocalised structure of benzene?
in benzene, all 6 C-C bonds are the same length, intermediate b/w single & double bonds (0.139nm)
in 1,3,5-cyclohexatriene, there are 3 longer C-C bonds 0.154nm & 3 shorter C=C bonds 0.134nm
how do addition reactions give evidence for the delocalised structure of benzene?
benzene reacts very slowly & needs a catalyst
so substitution reactions occur in preference to addition
1,3,5-cyclohexatriene readily undergoes electrophilic addition
bromine water turns from orange to colourless
how does enthalpy of hydrogenation give evidence for the delocalised structure of benzene?
cyclohexene + H2 –> cyclohexane enthalpy change = -120kJ
1,3,5-cyclohexatriene + 3H2 –> cyclohexane -360kJ
but hydrogenating benzene:
benzene + 3H2 –> cyclohexane -208kJ
–> benzene is more stable than 1,3,5-cyclohexatriene
benzene is 152kJ more stable than the triene
bc benzene has delocalised e-s
the 152kJ = delocalisation energy of the p e-s
what is the stability of cyclohexane?
most energetically stable compared w benzene & triene
how do aromatics react?
electrophilic substitution
what are the reagents, conditions & products of electrophilic substitution for nitration?
conc. HNO3 & conc. H2SO4
below 50C to minimise multiple substitutions
products: aromatic nitro compounds
what are aromatic nitro compounds used for?
to make aromatic amines –> azo dyes
to make explosives
what is the overall equation for electrophilic substitution (nitration)?
see booklet
what is the equation for making the electrophile in nitration (NO2+)?
HNO3 + H2SO4 –> NO2+ + HSO4- + H2O
what is the mechanism for electrophilic substitution (nitration)?
see booklet
at end show regeneration of catalyst: H+ + HSO4- –> H2SO4
what are the reagents, conditions & products of electrophilic substitution for Friedel-Crafts acylation?
acyl chloride & AlCl3
<50C, anhydrous to prevent reaction of AlCl3
products: aromatic ketones –> organic synthesis
what is the overall equation for electrophilic substitution (F-C acylation)?
see booklet
what is the equation for making the electrophile in F-C acylation?
see booklet
what is the mechanism for electrophilic substitution (F-C acylation)?
see booklet
at end show regeneration of catalyst: H+ + AlCl4- –> AlCl3 + HCl
compare Friedel-Crafts acylation with normal acylation
see table in booklet
be aware of F-C acylation with acid anhydrides - never come up before
see booklet
what are the different types of amines?
primary, secondary, tertiary
related to ammonia (NH3)
aromatic amines: N is directly bonded to the benzene ring
what are the interactions b/w amine molecules?
some hydrogen bonding but weaker than in alcohols
no H bonding b/w tertiary amines
compare the melting points of primary, secondary & tertiary amines & quaternary ammonium salts
primary & secondary: both have H bonding (&VDW) b/w molecules
secondary amine has higher mp bc larger so stronger VDW
tertiary: lowest mp bc no H bonding b/w molecules - only VDW b/w molecules
quaternary ammonium salt: highest mp - ionic interactions –> lattice
describe the structure of quaternary ammonium salts
no lone pair of e-s on N so do not behave like amines/ammonia
one dative covalent bond - N donates 2e-s
describe the preparation of aliphatic amines by reacting NH3 + halogenoalkanes
excess conc. NH3 in ethanol, high pressure in sealed container
equation: R-X + 2NH3 –> R-NH2 + NH4X
nucleophilic substitution mechanism
if conc. of halogenoalkane > conc. of NH3, further substitutions happen to form 2 & 3 amines then 4 ammonium salt.
if excess conc. NH3 used, 1y amine main product (but still mixture of products)
if excess halogenoalkane is used, 4y ammonium salt is main product
describe the preparation of aliphatic amines by reduction of nitrile compounds
only one amine formed, not a mixture
product has one more C atom than the starting material
1. formation of a nitrile from a halogenoalkane
2. reduction of the nitrile to form an amine
describe the formation of a nitrile from a halogenoalkane
R-X + KCN warm ethanol & water –> R-CN +KX
H2O dissolves ionic KCN
ethanol dissolves halogenoalkane
describe the reduction of the nitrile to form an amine
R-CN + 2H2 Ni catalyst & heat –> R-CH2-NH2
or R-CN + 4[H] LiAlH4 in ethoxyethane –> R-CH2-NH2
describe the preparation of 1y aromatic amines & equation
what would the product be if NaOH not added?
reduction of nitro compounds
tin & moderately conc. HCl followed by NaOH
see booklet for equation
4y ammonium salt - see booklet
how are amines Bronsted-Lowry bases?
Lewis bases?
proton acceptors
weak bases
bases bc lone pair of e-s on N atom can readily accept a proton
equilibrium reaction see booklet
e- pair donor
what does the ability of ammonia/amine to act as a base depend on?
how well the lone pair on N can accept H+
the higher the e- density of the lone pair on N, the better it can accept H+ –> so the stronger the base
what is the order of base strength?
3y amine > 2y amine > 1y amine > NH3 > aromatic amine
compare & explain the difference in base strength of 3y, 2y & 1y amines to ammonia
the more alkyl groups that are substituted onto the N atom,
the more electron density is pushed onto the lone pair on N
so the it is better at accepting H+
so the stronger the base
compare & explain the difference in base strength of ammonia & aromatic amines
the lone pair on N is delocalised into the benzene ring,
so it is less electron dense
so worse H+ acceptor
so weaker base
describe the successive nucleophilic substitution reactions of amines = further substitution
the amine product has a greater e- density on the lone pair on N so is better at reacting with the halogenoalkane than the original molecule
the H atoms on N are successively replaced by the R group from the halogenoalkanes to eventually form the quaternary ammonium salt
draw mechanism for formation of aliphatic amines
nuc. sub.
see booklet
describe the uses of quaternary ammonium salts
cationic surfactants
fabric softener
hair conditioner
ionic ‘head’ = hydrophilic
alkyl chain ‘tail’ = hydrophobic
state the equation & draw the mechanism for acylation of amines
nuc. addition-elimination
see booklet
replaces H on N with acyl group –> amide + HCl or carboxylic acid
2nd molecule reacts with HCl/carb. acid –> salt
what is the general structure of amino acids?
H2N-C-H-R-COOH
amine group, carboxylic acid group & variable R group
every amino acid exists as a Zwitterion
(20 naturally occurring AAs)
define Zwitterion
each amin group is protonated by a carboxylic acid group on another molecule
what attractions are there b/w Zwitterions?
ionic attraction
describe how amino acids show optical isomerism
amino acids (except glycine) have a chiral C atom with 4 different groups attached to it
so when the plane of polarised light is shone at them, it is rotated
only one of these enantiomers is present in nature
define primary structure of an amino acid
the sequence of amino acid units in the chain
define secondary structure of an amino acid
the chain of AAs is often arranged in a helix (or B-pleated sheets) = 2y structure
helix is held together by hydrogen bonds b/w C=O & H-N in adjacent spirals
there are many H bonds –> stable
define tertiary structure of an amino acid
the helix of AAs is folded into a specific 3D shape = 3y structure
caused by bonds b/w R groups: electrostatic/ionic interactions, H-bonds, disulfide bridges (& permanent dipole-dipole)
how does the amine group of an AA react?
protonated by acids
acylation with acyl chlorides & acid anhydrides
nucleophilic substitution with halogenoalkanes
how does the carboxylic acid group of an AA react?
deprotonated by bases
esterification with alcohols (with conc. acid catalyst)
how are peptides formed?
amino acids are joined together in condensation reactions to make dipeptides & polypeptides
- joined together by amide/peptide
draw diagram of dipeptide
2 forms
C=O-N-H in middle
how are peptides/proteins broken down?
hydrolysed into their constituent AAs
either with:
strong acid –> -NH3+
strong alkali –> -COO-
draw the structure of amino acids in alkali, neutral & acidic conditions
neutral = Zwitterion
see table in booklet
state how you can differentiate b/w stereoisomers of amino acids
optical isomerism
shine plane of polarised light at sample then observe which way it is rotated
each enantiomer will rotate it in opposite directions by the same amount
why is a polyester biodegradable?
is can be easily hydrolysed
define protein
series of amino acids joined by peptide link
how can amino acids be separated & identified?
thin layer chromatography
located on chromatogram by developing agents e.g. ninhydrin or UV
identified by Rf values
draw disulfide bridge b/w 2 cysteine groups
-S-S-
describe active sites of enzymes
stereospecific - specific geometry that allows substrate to bind e.g. with H bonds
only one enantiomer can bind
binds to substrate molecule
define enzyme
proteins that act as catalysts in biological systems
drugs can be…
enzyme inhibitors that bind to active site
how can such drugs be designed?
using computers
what is a nucleotide made up of?
a phosphate ion bonded to 2-deoxyribose which is bonded to 1 of the 4 bases adenine, cytosine, guanine & thymine
draw part of the DNA backbone
see booklet
draw nucleotide with each of the 4 bases
see booklet
draw how a cytosine unit H bonds to guanine unit
see booklet
draw how a thymine unit H bonds to adenine unit
see booklet
describe the structure of DNA
a single strand of DNA (deoxyribonucleic acid) is a polymer of nucleotides linked by covalent bonds b/w the phosphate group of one nucleotide and the 2-deoxyribose of another nucleotide
this forms a sugar-phosphate-sugar-phosphate polymer chain with bases attached to the sugars
2 complementary strands are arranged as a double helix
what is 3 prime & 5 prime in DNA?
the # of carbon atom that the phosphate group is bonded to
draw cis-platin
see booklet
same group same side
explain how cis-platin acts as an anti-cancer drug
stops DNA replication in cancer cells by ligand replacement reaction with DNA:
Cl ligands are replaced
in which a bond is formed b/w platinum & a nitrogen atom on 2 guanines on different DNA strands at 90degrees
–> binds strands together so cannot be separated
society needs to assess the balance between the benefits and the adverse effects of drugs, such as the anticancer drug cisplatin
draw trans-platin & explain why this would not stop DNA replication
see booklet - same groups on opposite sides
trans-platin has the wrong geometry, as Cl atoms are 180 apart, to bind to 2 guanines on opposite strands
so cannot hold DNA strands together
define addition polymers
long chain molecules made from joining many short molecules (monomers) together with no other products
what are the monomers for addition polymers
alkenes
molecules with C=C
examples of addition polymers
poly(ethene)
PVC
poly(propene)
what is the biodegradability of addition polymers & why?
non-biodegradable
due to absence of polar bond in the main chain - all bonds are C-C
define condensation polymers
long chain molecules made from joining many shorter molecules (monomers) together with another small molecule also formed e.g. water, HCl, NH3
how are condensation polymers formed?
by reactions b/w dicarboxylic acids & diols
dicarboxylic acids & diamines
amino acids
what are the repeating units & linkages b/w them in polyesters e.g. terylene
dicarboxylic acid + diol
water released
-O-C=O
see booklet
what are the typical uses of polyesters e.g. terylene
terylene is used as rope as it is tough & strong
other polyesters can be used as clothing fabric
what are the repeating units & linkages b/w them in polyamides e.g. nylon 6,6 & kevlar
dicarboxylic acid + diamine w water released
or polymerisation of amino acids bc they have carboxyl & amine group
NH-C=O
amide linkage
see booklet
what are the typical uses of polyamides e.g. nylon 6,6 & kevlar
strength
nylon 6,6 - clothing fabric
kevlar - bulletproof vest
describe the IMF b/w molecules of condensation polymers
H bonds
permanent dipole-dipole
draw repeating unit from monomer structure & from section of polymer chain
draw structure of monomer from section of polymer
describe the hydrolysis of condensation polymers
can be hydrolysed back to constituent molecules by the addition of H2O
H2O attracted to polar regions - polar bonds
links are broken
what is the biodegradability of condensation polymers & why?
biodegradable
polar C-N or C-O bonds in the main chain can be broken down easily
